1. Field of the Invention
The present invention relates to a photo film cassette. More particularly the present invention relates to an improvement of light-trapping ribbons disposed in a photo film cassette.
2. Description of the Related Art
A known photo film cassette has a cassette shell, a rotatable spool, and photo film wound on the spool and contained in the cassette shell. A passage port is formed in the cassette shell. The passage port communicates to the exterior of the cassette, and allows the photo film to pass into and out of the cassette shell. Light-trapping ribbons are disposed inside the passage port for preventing ambient light from entering the cassette shell and thus preventing the photo film from being exposed or fogged.
The known light-trapping ribbons are made of a soft and flexible material to protect surfaces of the photo film from being scratched during passage through the passage port. An example of such ribbons are pile woven fabrics, constituted of a base fabric and pile threads rooted therein. An example of weave of such a pile woven fabric is disclosed in JP-A (Japanese Patent Laid-open Publication No. 2-15254). One warp pile thread of this ribbon is passed under one weft thread, and retained on the warp pile woven fabric. Beside the warp pile thread, first and second warp threads are arranged in parallel and contact the pile thread. Structurally, one weft thread is passed over the first warp thread, and then passed over the warp pile thread, before being passed over the second warp thread.
However, the retention of the warp pile thread on the above-mentioned fabric is somewhat weak. The warp pile thread passes under the weft thread in a fashion common to either of the adjacent warp threads, and is likely to be moved by incidentally applied force. When a needle loom is used for weaving the warp pile woven fabric, warp pile threads are often accidentally placed on the base of an improper position. A position where a pile thread is missed, i.e., not present, will have a hole. Holes can cause failure of the light trapping characteristics of the pile woven fabric.
It is also known to apply a filler agent to a bottom face of the pile woven fabric to prevent bottom portions of the pile threads from dropping away from the base fabric. It is conceivable to use a filler having a high wettability, i.e., a characteristic of easily permeating into the fabric, for the purpose of ensuring adhesion of the filler to the fabric, especially in fabrics where the bottom of the pile threads does not project from, but is flush with, the bottom of the base fabric.
However, there are disadvantages associated with the use of such a filler, because the filler applied to the bottom face permeates into top portion of the pile threads, and hardens the pile threads which contact with the photo film. The surfaces of the photo film thus tend to be scratched by the hardened pile threads of the ribbons during passage through the passage port.
U.S. Pat. No. 4,634,306 and U.S. Pat. No. 4,846,418 disclose a leader-advancing photo film cassette, in which a leader of the photo film is entirely pre-contained in a cassette shell, and when a spool is rotated, the leader is advanced to the outside of the cassette shell. It is conceivable to provide the leader-advancing cassette with light-trapping ribbons. However, conventional light-trapping ribbons have pile bottoms flush with a bottom face. Therefore, the filler hardens pile threads until the pile threads become resistant to the movement of the photo film. The leader of the photo film is thus hindered from advancing through the passage port. Also, the film is likely to be scratched.